My Cargo 7 shows error E21 and the motor won't assist. What should I check?

E21 is a motor sensor error, usually caused by the motor connector. Turn the bike off, find the connector on the chainstay a few inches up from the rear axle, and slide back the rubber cover. Check that the two halves' arrows line up and that the pins aren't bent, green, or wet. Clean out any dirt with a dry cloth, then push the connector together until it seats fully. Turn the bike off for about 10 seconds and back on. If E21 stays on, it's likely the sensor or cable, which is covered under warranty repair.